Algae Color is a term used to describe the various colors of algae found in nature. Diatoms are microscopic, single-celled organisms that are often found in aquatic environments and have a silica shell that can be yellow, brown, or green. ABALONE are mollusks with a shell that can range from green to blue to purple. DIATOM is another term for a single-celled organism, and AGAR is a type of algae that is often used in food products and has a RED color. Marinegreen is a type of algae that is typically found in saltwater and has a green hue.